1. Field of the Invention
The present invention relates to matrix display devices, and more particularly to driving system for a matrix display device having display elements of high density.
2. Description of the Prior Art
Matrix panel display devices using liquid crystal or the like have been developed recently. These are generally classified into so-called active matrix to form active elements on a panel and passive matrix not to form them.
The former has memory function on a panel and can be multiplexed at high rate. However, technology to form the active elements of high performance uniformly throughout a large area is very difficult, and, if possible, may result in the high cost.
On the other hand, the latter has no active element but compensates low multiplexing property of the liquid crystal display element by wiring technique and driving manner only thereby it can realize density to certain degree and is low in cost. A television using passive matrix of 120 rows and 160 columns is now in practice.
Video signals for televisions are most used now among picture signals. For example, NTSC system in Japan transmits information of 525 rows halved into two fields of odd rows and even rows by means of interlaced scanning.
Since an existing liquid crystal television of 120 rows does not perform interlaced scanning but does superposition display on the same picture element by both even and odd fields, above-mentioned system is effective to about 260 lines.
However, in order to display the density more than 260 rows there is no method other than that information in the opposite field is stored in a memory and then called or that the display quality is sacrificed. In this connection, FIG. 1 shows an example of electrode arrangement of a liquid crystal display device in the prior art. In the figure, numerals S.sub.1, S.sub.2, S.sub.3 designate row electrodes to which are applied time sharing timing signals such as .phi..sub.1, .phi..sub.2, .phi..sub.3 shown in FIG. 2 respectively, D.sub.A 1, D.sub.A 2, D.sub.A 3 designate column electrodes to which is applied data signal such as d.sub.A 1 on the basis of display data of odd row, and D.sub.B 1, D.sub.B 2, D.sub.B 3 designate column electrodes to which is applied data signal such as d.sub.B 1 on the basis of display data of even row. The liquid crystal display element is grasped between both row and column electrodes and driven.
The display elements in FIG. 1 are arranged in 6 rows and 3 columns, but the electrodes are in 3 rows and 6 columns reversely. Such method of driving display elements of N.times.M in N rows and M columns by wiring technique in N/m rows and m.M columns is generally called multiple matrix. Where m represents multiplicity and FIG. 1 is an example of double matrix at m=2.
Reason why multiple matrix is used is in low multiplexing property of the liquid crystal display element. Display quality of liquid crystal, i.e. contrast or angle of view field is reduced as the multiplexing rate n is increased. Depending on the criterion, it seems that n=60 in the present and n=100 in future. Therefore at n=60 display of 120 rows is attained by double matrix and display of 480 rows is by matrix of eight times.
FIG. 3 shows another example of electrode arrangement of a liquid crystal display device in the prior art. Display elements are divided into upper half a and lower half b, and each half has the same electrode arrangement as that shown in FIG. 1 but the electrodes are taken out from either upper side or lower side in place of the alternate taking. Arrangement in FIG. 3 is referred to as so-called "up-and-down taking". Problem produced at increasing the multiplicity m is complication of the multiple wiring accompanied with reduction of the aperture ratio and increase of the manufacturing cost.
The up-and-down taking is favorable because the multiplicity in wiring being half of that in drive will do. In FIG. 3, for example, multiplicity of four times is used in drive but double up-and-down taking is used in wiring. Using this method, if display of 480 rows is attained by multiplicity of eight times in drive, it is done by up-and-down taking of multiplicity of four times in wiring.
Using above-mentioned devices in the prior art, TV display of 480 rows in full field is possible. However, if serial video signal in interlaced scanning is used as it is, problem may occur. For example, in both FIG. 1 and FIG. 3, odd row and even row are constituted by the same row electrode. Consequently either of following two methods must be performed. One method is that signal in interlaced scanning is stored in a memory and then driven by timing transformation, and other method is that in the opposite field non-effective signal is entered to data signal.
In the former, at 480 rows, 640 columns and 16 tones for example, the memory is required at large amount of more than 1 mega bits. The latter is equivalent to the drive in the double multiplexing rate thereby the display quality is reduced. In order to maintain the display quality to similar degree, the multiplicity must be doubled.